No experience with the S5, but on the G9 I normally have the E-Stabilization on all the time (with native m4/3 lenses) - for me, the extra stability and reduced 'warping' effects with wide-angle lenses outweigh the small extra crop and marginal reduction in resolution. AFAIK yes it does use the gyro data. As Kye pointed out recently on another thread, you can still get motion blur due to camera movement, as the E-Stabilization part can't do anything about that, but I think Panasonic use a combination of lens, sensor shift and electronic stabilization (when E-stab is enabled), which should minimise that problem in theory.
Why not try it and see what you think?
(I also use stabilization in post - Mercalli v5 in my case - but every software stabilizer I've ever tried or used can be 'broken' by some material - I think it's far better to stabilize in camera as much as possible).